152 Dr.,- Herschel’s Experiments for Investigating 
the transmitted colours, must be exactly equal to C t S, in 
which it is to be placed, that the blue bow may be seen. But 
these angles in my red bow, are not the same as they are in 
the Newtonian blue one; for, in figure 2, the angle t s p } 
which the red bow subtends, is 5 , 55 / ',4 less than the angle 
t S pm figure 3, subtended by the Newtonian blue one ; and 
the position of the eye Cts, in figure 2, for seeing the vertex 
of the red bow, is 15' 46" less than C t S figure 3, in which 
position the eye sees the vertex of the blue bow. Now as 
these angles arise immediately out of the critical separation of 
the rays, it is evident that one of these bows cannot be the 
converse of the other, but that we have two critical separations 
essentially different, namely, the reflective and the intro- 
missive. 
Second consideration. The transmitted colours, which 
Newton makes visible by the addition of a second prism, 
cannot be seen without it. For, if the red, orange, and yellow 
rays, were not intercepted by the additional prism, they would 
be refracted at p r t, figure 1, and pass into the air, scattered 
in such a manner, as to be totally unfit for giving a distinct 
image. My red bow, on the contrary, may be seen in one 
prism, laid down in open daylight, just as we see the blue 
bow explained by Newton. 
Third consideration. The residuary colours of the New- 
tonian blue bow, being transmitted at p r t, the interposition 
of a second prism, will refract them downwards to s, for 
which reason, they can never be seen in the form of a red 
bow, by an eye placed above the prism at S, where the blue 
bow is visible ; whence it follows- that, if we were not now 
acquainted with an original red bow, all the phenomena of the 
